Annular fluids or packer fluids are liquids which are pumped into annular openings such as, for example, (1) between a wellbore wall and one or more casing strings of pipe extending into a wellbore, or (2) between adjacent, concentric strings of pipe extending into a wellbore, or (3) in one or both of an A- or B-annulus in a wellbore comprising at least an A- and B-annulus with one or more inner strings of pipe extending into a said wellbore, which may be running in parallel or nominally in parallel with each other and may or may not be concentric or nominally concentric with the outer casing string, or (4) in one or more of an A-, B- or C-annulus in a wellbore comprising at least an A-, B- and C-annulus with one or more inner strings of pipe extending into a said wellbore, which may be running in parallel or nominally in parallel with each other and may or may not be concentric or nominally concentric with the outer casing string.
Yet alternatively, said one or more strings of pipe may simply run through a conduit or outer pipe(s) to connect one or more wellbores to another wellbore or to lead from one or more wellbores to a centralized gathering or processing center; and said annular fluid may have been emplaced within said conduit or pipe(s) but external to said one or more strings of pipe therein. Insulating annular fluids or insulating packer fluids are annular fluids or packer fluids used to control heat loss—both conductive and convective heat losses.
Further, conditions where the drill string are in contact with large bodies of water, such as deepwater operations, may also require thermal isolation of production fluids from the surrounding environment. Deepwater drilling is carried out under high bottom hole temperatures and pressures. The deepwater wells stretch to several thousand meters in depth, where the majority of the well string is in direct contact with ocean waters. Contact of the surrounding waters with the drill string may result in the rapid transfer of heat, leading to the formation of gas hydrates as described above.
Heavy oil production is another operation which often can benefit from the use of an insulating annular fluid. In heavy oil production, a high-pressure steam or hot water is injected into the well and the oil reservoir to heat the fluids in the reservoir, causing a thermal expansion of the crude oil, an increase in reservoir pressure and a decrease of the oil's viscosity. In this process, damage to the well casing may occur when heat is transferred through the annulus between the well tubing and the casing. The resulting thermal expansion of the casing can break the bond between the casing and the surrounding cement, causing leakage. Accordingly, an insulating medium such as a packer fluid may be used to insulate or to help insulate the well tubing. The packer fluid may also reduce heat loss and save on energy requirements in stimulation using hot-water or steam (huff-n-puff) or in hot-water or steam-flooding.
In addition to steam injection processes and operations which occur as production through a permafrost layer or subsea fields such as in deep water (e.g., 1,500 to more than 6,000 feet), specially designed systems may require an insulating annular or packer fluid. For example, a subsea oil reservoir temperature may be from about 120° F. and 250° F., while the temperature of the water through which the oil may be conveyed is often as low as 32° F. to 50° F. Conveying the high temperature oil through such a low temperature environment can result in oil temperature reduction and consequently the separation of the oils into various hydrocarbon fractions and the deposition of paraffins, waxes, asphaltenes, and gas hydrates. The agglomeration of these oil constituents can cause blocking or restriction of the wellbore, resulting in reduction or even failure of the production operation.